JPH07297071A - Multilayered grain boundary insulated semiconductor ceramic capacitor - Google Patents

Abstract

PURPOSE:To restrain the defects inside a sintered body, by making at least the uppermost layer and the lowermost layer of inner electrode layers in a laminate be reinforcing electrode layers which are not electrically connected with outer electrodes. CONSTITUTION:An SrTiO3-Nb2O5-SiO2 based green sheet is cut so as to have a specified size. An inner electrode layer 2a and a reinforcing layer 2b composed of NiO and Li2O3 are screen-printed in a specified size on the green sheet 1. The green sheets 1 are arranged in the upper part and the lower part. Between them, a plurality of the green sheets 1 on which the inner electrode layers 2a are printed, and the green sheets 1 on which the reinforcing electrode layers 2b are printed are stacked, and pressed and fixed by pressure while heated. After the molded object is degreased and calcinated in the air, lower layer part outer electrode layers 3a of the same component as the inner electrodes 2a and the reinforcing electrode layer 2b are spread on both ends of the molded object, and baked in a reducing atmosphere. An upper layer part outer electrode layer 3b of Ag is spread on the lower layer part outer electrode 3a, and printed in the air to obtain a multilayered ceramic capacitor having varistor function.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention normally serves as a capacitor for absorbing low-voltage noise and high-frequency noise, while exhibiting a varistor function when high voltage such as pulse or static electricity enters. The present invention relates to a laminated grain boundary insulation type semiconductor ceramic capacitor used for the purpose of protecting semiconductors and electronic devices from abnormal voltages such as noise, pulses and static electricity generated in electronic devices.

[0002]

2. Description of the Related Art Conventionally, for example, a mixture of a semiconductor component and a MnO ₂ --SiO ₂ -based component in SrTiO ₃ with excess Ti is used to form a ceramic green sheet, and Ni or N is used.
An internal electrode was formed by dissolving at least one kind of low-valence Li, Na and K atoms in a compound containing an i atom. Then, a laminated body in which the ceramic green sheets and the internal electrodes are laminated so that the internal electrodes are alternately led out to the opposite end surfaces of the ceramic green sheets, and an external electrode provided so as to electrically connect the led out internal electrodes To form a monolithic ceramic capacitor.

[0003]

SUMMARY OF THE INVENTION In the above conventional configuration,
Due to the difference in volume change between the ceramic material and the internal electrode material during firing, there is a problem that delamination, internal electrode breakage, sintering failure and the like are likely to occur inside the sintered body.

Therefore, an object of the present invention is to solve the above-mentioned conventional problems and to provide an excellent laminated type grain boundary insulation type semiconductor ceramic capacitor having almost no defects inside the sintered body.

[0005]

In order to achieve this object, a laminated grain boundary insulation type semiconductor ceramic capacitor of the present invention has a laminated body in which at least the uppermost layer and the lowermost layer of internal electrode layers are electrically connected to external electrodes. The reinforcing electrode layer is not connected to.

[0006]

According to the above structure, by providing the reinforcing electrode layer, the residual stress due to the difference in volume change during firing is relieved and the occurrence of defects inside the sintered body can be suppressed.

[0007]

EXAMPLES An example of the present invention will be described in detail below.

FIG. 1 is a partially cutaway perspective view of a laminated grain boundary insulation type semiconductor ceramic capacitor (hereinafter referred to as a laminated ceramic capacitor having a varistor function) according to an embodiment of the present invention. FIG. 2 is an exploded perspective view of a laminated body of a laminated ceramic capacitor with a varistor function according to an embodiment of the present invention. FIG. 3 is a diagram showing a manufacturing process of a monolithic ceramic capacitor with a varistor function in one embodiment of the present invention.

First, SrTiO ₃ (Sr / Ti = 0.9
7): 97 mol%, Nb ₂ O ₅ : 1 mol%, Mn
A raw sheet having a composition of O ₂ : 1 mol% and SiO ₂ : 1 mol% and having a thickness of 25 μm was prepared by a doctor blade method or the like, and the raw sheet was cut into a predetermined size.

Then, on the green sheet 1 cut into a predetermined size, NiO: 99.9 mol%, Li ₂ CO ₃ :
Internal electrode layer 2a and reinforcing electrode layer 2 having a composition of 0.1 mol%
b was screen-printed to a predetermined size.

As is apparent from FIG. 2, the uppermost and lowermost raw sheets 1 which are ineffective layers are not printed with the internal electrode layers 2a and the reinforcing electrode layers 2b, and are usually laminated in plural layers. Further, at this time, the internal electrode layers 2a are printed so as to reach the opposite (different) edges alternately, as is well known.
Moreover, the reinforcing electrode layer 2b was printed so as not to be connected to the lower layer external electrode 3a. After that, the green sheets 1 are arranged on the upper and lower sides, and a plurality of the green sheets 1 on which the internal electrode layers 2a are printed and the green sheets 1 on which the reinforcing electrode layers 2b are printed are laminated between them and heated while heating. A compact was obtained by pressure and pressure bonding.

Next, the molded body was heated in air at 1100 ° C.
Degreasing and calcination were performed in 2 hours. After the calcination, a lower external electrode layer 3a having the same composition as the internal electrode layer 2a and the reinforcing electrode layer 2b was applied to both ends of the molded body. After application, N ₂ : H ₂ = 9
Baking was performed at 1230 ° C. in a 9: 1 reducing atmosphere. After firing, the upper layer external electrode layer 3b made of Ag was applied on the lower layer external electrode and baked in air at 800 ° C. for 1 hour to obtain a multilayer ceramic capacitor 4 with a varistor function.

The shape of the monolithic ceramic capacitor with a varistor function in this embodiment is L × W in FIG.
XH is called 2.0 type of 2.0x1.25x0.85mm, 3 internal electrode layers 2a, reinforcing electrode layer 2
b is laminated one layer each on the upper and lower sides and two layers each on the upper side. The area of the reinforcing electrode layer 2b is the same as the internal electrode layer 2a.
The area is about 1.3 times. Further, the distance between the reinforcing electrode layer 2b and the internal electrode layer 2a was made equal to the distance between the internal electrode layers 2a.

Regarding the monolithic ceramic capacitor with a varistor function thus obtained, its capacitance, tan
Various electrical characteristics such as δ, varistor voltage, voltage non-linearity index α, high temperature and humidity applied load life characteristics in humidity, and Vickers indentation hardness inside the sintered body are also described in the following (Table 1).

[0015]

[Table 1]

Regarding the various electrical characteristics, the following measured values are shown. ◇ Capacitance C is a value at a measurement voltage of 1.0 V and a frequency of 1.0 kHz. ◇ The varistor voltage V _0.1mA is the value when the measurement current is 0.1mA. ◇ Voltage non-linearity index α is measured current 0.1mA and 1.0m
From the value at A, it was calculated from the formula α = 1 / log (V ₁ / V _0.1 ). ◇ Humidity and high temperature applied load life characteristics ΔV _0.1mA is 85 ℃, 85
% Change rate of varistor voltage V _{0.1 mA} after a 5.4 V direct current was loaded for 500 hours in an atmosphere of 100%.

For comparison, the same measurement was performed on a conventional laminated ceramic capacitor with a varistor function in which no reinforcing electrode layer was inserted.

It can be seen from Table 1 that both the varistor function and the capacitor function are stably exhibited when the reinforcing electrode layer 2b is inserted. Further, from the observation of the inside of the sintered body, it can be seen that the hardness is about doubled and the mechanical strength is also improved. Furthermore, no breakage of internal electrodes or delamination was observed at all. Therefore, the product of the present invention is suitable as a ceramic capacitor with a varistor function for protecting semiconductors and electronic devices from abnormal voltages such as noise, pulses, and static electricity generated in electronic devices.
In comparison, when the conventional reinforcing electrode layer was not inserted, stable electrical characteristics were not obtained, and delamination and internal electrode breakage occurred frequently inside the sintered body.

Further, the features of the reinforcing electrode layer obtained in the experiment conducted in carrying out the present invention will be described.

(1) The strength of the sintered body was improved by inserting a plurality of reinforcing electrode layers 2b, rather than inserting one layer above and below.

It is considered that this is because the residual stress is easily relaxed by increasing the number of the reinforcing electrode layers 2b.

(2) When the reinforcing electrode layer 2b was provided so as not to be connected to the external electrode, the variation in the capacitance component was small and a stable value was shown.

In general, as a method of connecting to the external electrode and not expressing the capacitance component, it can be easily imagined that the reinforcing electrode layer 2b is set to the same potential as the adjacent internal electrode layer 2a. However, in this case, stray capacitance appears and has a capacitance larger than the design value. The value of the stray capacitance varies widely depending on the sintered body element and does not always show a constant value.

(3) The internal structure of the sintered body was more uniform when the distance between the reinforcing electrode layer 2b and the internal electrode layer 2a was equal to or wider than the distance between the internal electrode layers 2a.

This is because when the interval is narrow, the sintering of the portion progresses to form a non-uniform structure such as sintering unevenness, and it is difficult for the electrical characteristics to be expressed and variations occur frequently.

(4) It is desirable that the raw material composition for the reinforcing electrode and the raw material composition for the internal electrode are the same. The reason for this is that in the case of heterogeneous materials, sintering unevenness is likely to occur inside the sintered body, as in (3) above.

The characteristics of the reinforcing electrode layer 2b have been described above from the viewpoint of initial characteristics and sintered body structure.
It is described from the viewpoint of life characteristics.

In general, since the semiconductor ceramic element has a relatively large porosity, it may have a problem that moisture easily penetrates and the moisture resistance life characteristic is easily deteriorated.
Even this monolithic ceramic capacitor with a varistor function has a problem that the moisture resistance and life characteristics are easily deteriorated. Therefore, when the reinforcing electrode layer 2b shown in the present invention is provided, moisture penetrates up to the reinforcing electrode layer 2b but does not reach the effective layer, and the reinforcing electrode layer 2b exhibits a moisture blocking effect, and as a result, moisture resistance life characteristics. It was found that the deterioration of
Therefore, as a new feature, (5) the reinforcing electrode layer 2b exhibits a moisture blocking effect. In this case, a plurality of layers are more effective than one layer provided on each of the upper and lower sides.

(6) When the area of the reinforcing electrode layer 2b is equal to or larger than the area of the internal electrode layer 2a, the effect of improving the moisture resistance is further improved. I found the above.

The varistor function-equipped monolithic ceramic capacitor manufactured by paying attention to the above (1) to (6) has a large capacity, a large voltage non-linearity index α, and excellent moisture resistance and life characteristics. , Usually acts as a capacitor to absorb low-voltage noise and high-frequency noise,
On the other hand, when a high voltage such as pulse or static electricity invades, it exhibits a varistor function and exhibits excellent responsiveness to abnormal voltage such as noise, pulse, static electricity, etc., conventional film capacitors, multilayer ceramic capacitors, semiconductor ceramic capacitors. It is expected to change to.

Further, the monolithic ceramic capacitor with a varistor function of the present invention is small in size and has a large capacity and high performance as compared with the conventional single plate type ceramic capacitor with a varistor function, so that it is used as a mounting component. The application of is also highly expected.

[0032]

As described above, in the laminated grain boundary insulating semiconductor ceramic capacitor of the present invention, at least the uppermost layer and the lowermost layer of the internal electrode layers in the laminated body are the reinforcing electrode layers.

As a result, the residual stress due to the difference in volume change between the ceramic layer and the internal electrode layer at the time of firing can be relaxed, and the occurrence of defects inside the sintered body can be prevented.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a laminated grain boundary insulation type semiconductor ceramic capacitor according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view of a laminated body according to an embodiment of the present invention.

FIG. 3 is a manufacturing process diagram of a laminated type grain boundary insulation type semiconductor ceramic capacitor according to an embodiment of the present invention.

[Explanation of symbols]

 1 Raw Sheet 2a Internal Electrode Layer 2b Reinforcing Electrode Layer 3a Lower Layer Ni External Electrode 3b Upper Layer Ag External Electrode 4 Multilayer Grain Boundary Insulation Semiconductor Ceramic Capacitor

Claims (3)

[Claims] 1. A laminated body, in which ceramic layers and internal electrode layers are alternately stacked, and an external electrode for electrically connecting the internal electrode layers of the laminated body, and at least the innermost electrode layer of the laminated body is provided. A laminated grain boundary insulation type semiconductor ceramic capacitor having upper and lowermost layers as reinforcing electrode layers which are not connected to the external electrodes. 2. The laminated grain boundary insulation type semiconductor ceramic capacitor according to claim 1, wherein the distance between the reinforcing electrode layer and the internal electrode layer is equal to or wider than the distance between the internal electrode layers. 3. The laminated grain boundary insulation type semiconductor ceramic capacitor according to claim 1, wherein the area of the reinforcing electrode layer is equal to or larger than the area of the internal electrode layer.